As a rule, a processing apparatus for photographic sheet material comprises several vessels each of which contains a treatment liquid, such as a developer, a fixer and a rinse liquid. As used herein, the term sheet material includes not only photographic material in the form of cut sheets, but also in the form of a web unwound from a roll. The sheet material to be processed is transported through these vessels in turn, by transport means such as one or more pairs of drive rollers, and thereafter optionally to a drying unit. The time spent by the sheet material in each vessel is determined by the transport speed and the dimensions of the vessel in the sheet feed path direction.
Apparatus for the processing of photographic sheet material such as aluminium lithographic printing plates is known, for example from EP-A-410500 (Agfa Gevaert NV), comprising a plurality of treatment vessels mounted one beside another to define a substantially horizontal sheet material path through the apparatus. Each vessel comprises a housing having a sheet material inlet and a sheet material outlet. The inlet and outlet are each closed by a pair of rotatable path-defining rollers biased into contact with each other to form a nip there-between through which the sheet material path extends.
The path-defining rollers are used to remove excess treatment liquid from the sheet as it passes from one treatment vessel to the next. This reduces carry-over of treatment liquid and thereby reduces contamination and wastage. A good removal of processing liquid is also required to reduce the drying time of the sheet material after the last process bath, and hence to reduce the energy use.